In recent years there has been a considerable effort spent in the design and fabrication of a suitable intravenous delivery pump that is positive in its operation to force intravenous feeding fluid into the blood vessels of a patient. It has been found that the positive pumping of the parenteral fluid has many advantages over the older gravity feed that has been used for many years. Insofar as the present invention is concerned, the advantages of such pumps need not be discussed. It is sufficient to note that several pumps have been proposed and one or two have been accepted by the medical profession. U.S. Pat. No. 3,798,982, issued Mar. 26, 1974, by one of the present applicants, discloses a pump actuator that is adjustable both as to the timing of the pulses of its operation and the length of each pump stroke (hence the amount of fluid to be delivered at each stroke) over a considerable range of values, with a net result that the pumping of parenteral fluid could be modified over a considerable variety of values, such as from 5 to 1,500 milliliters per hour.
The present invention is designed as a timer for the pump actuator disclosed in said patent, so that when it is required it can be set to deliver the parenteral fluid for a particular period of time up to four hours (in the preferred form of the invention). Thereafter, an alarm could be operated to notify the nursing staff that the period of time had expired, or it could be set to stop the pump actuator as by breaking a switch in the power line to the actuator motor. One of the problems of intravenous feeding is the body's natural ability to "seal off" outside substances, in this case the injection needle. Obviously, a doctor wants to avoid inserting a different needle for each injection. However, in order to avoid using many needles, it is necessary to do something to prevent clogging of the bore of the needle. We propose to avoid clogging while maintaining sterile conditions (although using a single injection needle for a prolonged period) by maintaining a "keep open" flow of fluid under such pressure as to keep the neeedle open, but at a greatly reduced rate of flow. Preferably, the actuator is driven by a two-speed motor in which the power drive has a specific speed for normal operation, such as 10 r.p.m., and an auxiliary speed of approximately one-tenth that value. In this preferred form the motor is automatically switched from the preferred operating speed to a speed of one-tenth that amount when the predetermined time has elapsed, and an alarm is actuated (for example, a warning light is operated, but a signal could be sounded at the nurses station). This form provides that after the selected period of time is expired, the pump will continue to operate at the reduced rate so as to prevent clogging of the needle that has been inserted into the patient's veins.